Addons and current data amounts

[Antacid]

Let's say I have 5$ of data accidentally downloaded this month (from testing out the browser and such)

If I were to add the 10$ 100mb addon, would that dissolve my 5$ of data downloaded already? Or does it just ad on to it? 5$ plus any data after it is free (till 100mb).

[captain planet]

It would only take effect after you add it... unless you did it on the same day and slipped through the cracks you're probably getting charged. They'll pro-rate it though (i.e. if you add it on day 15 of your 30-day billing cycle you'll pay 5 bucks of data + half of 10 bucks for the add-on)